Tire comprising a hydrophilic polymer and elastomeric composition employed therein

ABSTRACT

An elastomeric composition includes at least one elastomeric diene polymer, at least one thermoplastic polymer, and at least one polymer comprising functional groups. The at least one thermoplastic polymer comprises a main hydrocarbon chain. Hydrophilic groups are linked to the main hydrocarbon chain. The functional groups are reactive with the hydrophilic groups. The composition may also include at least one reinforcing filler. The at least one reinforcing filler may include carbon black, silica, or both carbon black and silica. The composition may further include a silica coupling agent, a sulfur-based vulcanizing agent, or both a silica coupling agent and a sulfur-based vulcanizing agent. A tire for vehicle wheels including at least one element including an elastomeric material, where the at least one element include the composition, is also disclosed.

DESCRIPTION

[0001] The present invention relates to a tire for vehicle wheels and toan elastomeric composition. More particularly, the present inventionrelates to a tire for vehicle wheels comprising at least one elementmade of a cross-linked elastomeric material including a hydrophilicpolymer, and to an elastomeric composition comprising a hydrophilicpolymer.

[0002] In the rubber industry, in particular in the manufacture of tiresfor vehicle wheels, the use is known of elastomeric compositions whereinreinforcing fillers have been incorporated in the polymer base, in orderto improve the characteristics of the cross-linked product, inparticular mechanical properties and abrasion resistance. Thanks to itshigh reinforcing efficiency, carbon black is the most widely employedreinforcing filler. However, carbon black imparts to the cross-linkedproduct marked hysteretic characteristics, i.e. an increase of heatdissipated in dynamic conditions, which, as is known, causes, in thecase of a tire, an increase in the rolling resistance of the tireitself. This leads to an increase of the fuel consumption of thevehicles, and hence of both locomotion costs and air pollution. It ispossible to try to reduce such adverse effects by employing smalleramounts of carbon black and/or a carbon black having a smaller surfacearea. This inevitably leads to a reduction of the reinforcing action,with a worsening of the mechanical properties and of the abrasionresistance of the final product.

[0003] In order to reduce the hysteretic characteristics of thecross-linked products it is known to use the so-called “white”reinforcing fillers, such as gypsum, talc, kaolin, bentonite, titaniumdioxide, silicates of various types and especially silica, whichreplaces carbon black either entirely or partly. In this regard, see forexample European patent EP-501,227.

[0004] The use of silica-based reinforcing fillers involves severaldrawbacks, substantially related to the poor affinity of the same withrespect to the elastomers commonly used in the tire manufacture. Inparticular, to obtain a good dispersion degree of silica within thepolymer matrix it is necessary to submit the elastomeric compositions toan extensive thermal-mechanical mixing action. To increase the affinitybetween silica and the elastomeric matrix, it is necessary to employsuitable coupling agents, for instance sulfur-containing organosilaneproducts. However, the need of using such coupling agents sets a limitto the maximum temperature that can be reached during mixing andthermal-mechanical processing operations, on pain of an irreversiblethermal degradation of the coupling agent.

[0005] Therefore, it is still strongly felt the need of introducing inthe rubber compositions for tires new fillers which impart to the endproduct performances at least comparable to those obtained withconventional fillers, but without showing the drawbacks mentionedhereinabove. Said fillers should also be able to modulate theperformances of the finished product as a function of use conditions.

[0006] In the prior art, it was for instance suggested to introducehydrophilic polymers in elastomeric compositions, particularly in therubber compositions used for the manufacture of tire treads, in order toincrease the road grip of the tire, in particular on wet or icedgrounds.

[0007] For instance, in Japanese patent application (Kokai) JP-H5-170976a tire is described which has an improved road grip on ice or snowgrounds, wherein the tread includes short fibers and from 1 to 15 phr ofpowdered polyvinylalcohol (phr=parts by weight per 100 parts by weightof rubber). The fibers, for instance cellulose or synthetic polymerfibers, are oriented along the circumferential direction of the tire, soas to impart anisotropic characteristics. Road grip on ice or snowsurfaces is improved by the presence of polyvinylalcohol particleswhich, when contacted with water, dissolve, leaving in the treadcavities which increase roughness and hence road grip of the tread. Theamount of polyvinyl alcohol powder should not exceed 15 phr, so as notto worsen wear resistance to an unacceptable extent. Besides, lowamounts of polyvinylalcohol are necessary not to increase treadstiffness and therefore not to worsen the road grip on dry grounds.

[0008] In European patent application EP-896,981, an elastomericcomposition for use in tire tread manufacture is described, whichincludes modified polyvinylalcohol, in the form of powder or fibers.Such modified polyvinylalcohol has polyoxyalkylene groups along thechain, which increase the water solubility of the polymer, hencepromoting dissolution of the same when the tread gets in touch with awet surface, leaving cavities in the tread itself and forming a stickylayer at the interface with the road surface which should increase thetire road grip.

[0009] The use of hydrophilic polymers deriving from starch inelastomeric compositions is described in U.S. Pat. Nos. 5,374,671 and5,545,680. In particular, such patents describe elastomeric compositionscomprising from 1 to 50 phr of a hydrophilic polymer having a glasstransition temperature (T_(g)) ranging from 150° C. to 0° C. dependingupon the absorbed amount of water. Such hydrophilic polymer is adestructured starch comprising amylose, amylopectine, or mixturesthereof. The presence of the destructured starch in a rubber compositionfor tire treads is said to increase traction on wet grounds, whilereducing at the same time rolling resistance on dry roads. Thedestructured starch may be homogeneously dispersed throughout theelastomeric matrix or, preferably, it is immiscible with the polymericmatrix so that it tends to form fibers, preferably oriented fibers,within said matrix. Since destructured starch is a hydrolyzable andbiodegradable polymer, its presence in a tire is said to increase itsbiodegradability. A grafting agent may be added to the rubbercomposition, in order to bind the hydrophilic polymer to the elastomericbase. No indications are given either about the grafting agent to beused, or on how to accomplish such grafting.

[0010] U.S. Pat. No. 5,672,639 describes an elastomeric compositionreinforced with a destructured starch combined with a plasticizercompatible with the destructured starch, so as to form astarch/plasticizer composite. With respect to destructured starch assuch, said composite is said to have a better miscibility in theelastomeric matrix and would therefore prevent the formation ofagglomerates of non dispersed starch. The plasticizer has a softeningpoint lower than the softening point of destructured starch. Inparticular, poly(ethylene-vinylalcohol) having a softening point lowerthan 160° C., preferably comprised between 90° and 130° C., may beemployed as a plasticizer. Other products which may be used asplasticizers include: ethylene/vinylacetate copolymers,ethylene/glycidylacrylate copolymers and ethylene/maleic anhydridecopolymers, cellulose acetate, diesters of dibasic organic acids, andthe like. To try to couple the starch/plasticizer composite with theelastomeric matrix, the addition of a coupling agent having a groupwhich reacts with the hydroxyl groups of the composite, and a groupcapable of interacting with the elastomeric matrix is suggested. To thisaim, the use of coupling agents normally employed in silica-containingrubber compositions, in particular an organosilane tetrasulfide, isindicated.

[0011] In the Applicant's perception, the elastomeric compositionsincluding a hydrophilic polymer should satisfy various requirements torender their use actually advantageous in the manufacture ofcross-linked products, and in particular tires. First of all, suchcompositions, once cross-linked, should be able to absorb significantamounts of water, so as to change the performance of the product whenthe latter gets in touch with water. On the other hand, the presence ofthe hydrophilic polymer should not jeopardize the basic characteristicsof the elastomeric cross-linked composition, e.g. tensile properties (inparticular, tensile stress at break, elongation at break and modulus),dynamic properties (in particular, dynamic modulus and tandelta), andabrasion resistance.

[0012] The Applicant has now found that it is possible to address theabove requirements by introducing in the elastomeric matrix athermoplastic polymer containing hydrophilic groups as definedhereinafter, combined with a polymer having groups reactive with saidhydrophilic groups. In this way, it is possible to produce an articlewherein the hydrophilic polymer is capable of absorbing significantamounts of water without dissolving and, therefore, being easily removedfrom the elastomeric matrix. Besides, the hydrophilic polymer is able toexert a reinforcing action on the elastomeric material, thus replacing,at least partially, the conventional reinforcing fillers, while keepingexcellent, both tensile and dynamic, mechanical properties.

[0013] In a first aspect, the present invention therefore relates to atire for vehicle wheels comprising at least one element made of anelastomeric material, characterized in that said element includes acomposition comprising:

[0014] (a) at least one elastomeric diene polymer;

[0015] (b) at least one thermoplastic polymer having a main hydrocarbonchain to which hydrophilic groups are linked;

[0016] (c) at least one polymer containing functional groups reactivewith said hydrophilic groups.

[0017] In a preferred aspect, said element including said composition isa tread belt.

[0018] In another aspect, the present invention relates to anelastomeric composition comprising:

[0019] (a) at least one elastomeric diene polymer;

[0020] (b) at least one thermoplastic polymer having a main hydrocarbonchain to which hydrophilic groups are linked;

[0021] (c) at least one polymer containing functional groups reactivewith said hydrophilic groups.

[0022] In the present description and claims, by the expression“thermoplastic polymer having a main hydrocarbon chain to whichhydrophilic groups are linked” (for the sake of brevity also“hydrophilic polymer”) it is meant a synthetic polymer whereinhydrophilic groups, either directly or through side groups, are linkedto the main hydrocarbon chain, either linear or branched, and free fromglycoside bonds. As known, glycoside bonds are ether bonds, cleavable byhydrolysis, deriving from polycondensation of monosaccharides, which aretypically present in polysaccharides such as starch and cellulose.

[0023] In the present description and claims, by “hydrophilic groups” itis meant groups which are able to bind water molecules by means ofhydrogen bonds.

[0024] According to a preferred embodiment, the hydrophilic polymer ispresent in the elastomeric composition in a quantity comprised between0.1 and 100 phr, preferably between 3 and 50 phr, even more preferablybetween 5 and 20 phr. As is known, “phr” means parts by weight per 100parts by weight of elastomeric base.

[0025] Preferably, the polymer containing functional groups reactivewith the hydrophilic groups (in the following also referred to, for thesake of brevity, “functionalized polymer”) is present in the elastomericcomposition in a quantity so as to obtain a weight ratio between thehydrophilic polymer and the functionalized polymer comprised between0.5:1 and 10:1, preferably between 1:1 and 5:1.

[0026] According to a preferred embodiment, said hydrophilic groups areselected from:

[0027] hydroxyl groups —OH;

[0028] carboxylic groups —COOH, possibly at least partially in the saltform;

[0029] ester groups —COOR (R=alkyl or hydroxyalkyl);

[0030] amide groups —CONH₂;

[0031] sulfonic groups —SO₃H, possibly at least partially in the saltform.

[0032] Preferably, the hydrophilic polymers according to the presentinvention are capable to absorb at least 0.1% by weight of water basedon the polymer weight, after a 24-hour exposure in an environment havinga 50% relative humidity at the temperature of 24° C. (according tostandard method ASTM D570).

[0033] Preferably, the hydrophilic polymers according to the presentinvention are thermoplastic products having a melting temperature lowerthat 230° C., preferably comprised between 200° and 130° C.

[0034] The hydrophilic polymers according to the present invention maybe selected in particular from: polyacrylic acid, polymethacrylic acid,polyhydroxyalkylacrylate, polyalkylacrylate, polyacrylamide,acrylamide/acrylic acid copolymers, polyvinylalcohol, polyvinylacetate,vinylalcohol/vinylacetate copolymers, ethylene/vinylacetate copolymers,ethylene/vinylalcohol copolymers, ethylene/vinylalcohol/vinylacetateterpolymers, polyvinyl-sulfonic acid, polystyrene sulfonate, andmixtures thereof.

[0035] According to a particularly preferred embodiment, saidhydrophilic polymer comprises repeating units having the formula

[0036] with a random or block distribution along the chain.

[0037] This preferred class of hydrophilic polymers encompasses:polyvinylalcohol, ethylene/vinylalcohol copolymers,ethylene/vinylalcohol/vinylacetate terpolymers. Polymers may also beused wherein the groups of formula (I) have been at least partiallymodified, for instance by partial acetylation with aliphatic aldehydes(as described, for instance, in U.S. Pat. No. 4,002,796).

[0038] The following are particularly preferred:

[0039] (i) vinylalcohol polymers obtained by hydrolysis ofpolyvinylacetate, with a hydrolysis degree comprised between 50 and 100mol %, preferably between 70 and 90 mol %;

[0040] (ii) ethylene/vinylalcohol copolymers having a content ofethylene units generally comprised between 20 and 60 mol %, preferablybetween 25 and 50 mol %.

[0041] Copolymers of type (i) are commercially available under thetrademarks Mowiol® (Clariant), Gohsenol® (Nippon Gohsei), Elvanol® (DuPont), Airvol® (Air Products). Copolymers of type (ii) are commerciallyavailable under the trademark Soarnol® (Atochem).

[0042] The polymer containing functional groups reactive with thehydrophilic groups employable in the present invention is generally athermoplastic hydrocarbon polymer in which functional groups have beenintroduced selected from: carboxylic groups, anhydride groups, estergroups, silane groups, epoxy groups. The amount of functional groupspresent in the polymer is generally comprised between 0.05 and 50 partsby weight, preferably between 0.1 and 10 parts by weight, based on 100parts by weight of the polymer.

[0043] The functional groups may be introduced during the production ofthe polymer, by co-polymerization with corresponding functionalizedmonomers containing at least one ethylene unsaturation, or by subsequentmodification of the hydrocarbon polymer by grafting said functionalizedmonomers in the presence of a free radical initiator (in particular, anorganic peroxide).

[0044] Alternatively, it is possible to introduce the functional groupsby reacting pre-existing groups of the hydrocarbon polymer with asuitable reagent, for instance by an epoxydation reaction of a dienepolymer containing double bonds along the main chain and/or as sidegroups with a peracid (for instance, m-chloroperbenzoic acid orperacetic acid) or with hydrogen peroxide in the presence of acarboxylic acid or a derivative thereof.

[0045] In particular, the base hydrocarbon polymer may be selected from:

[0046] (a) ethylene homopolymers or copolymers of ethylene with analpha-olefin having from 3 to 12 carbon atoms (preferably propylene or1-octene), comprising in general from 35 to 97 mol % of ethylene andfrom 3 to 65 mol % of alpha-olefin,

[0047] (b) propylene homopolymers or copolymers of propylene withethylene and/or an alpha-olefin having from 4 to 12 carbon atoms(preferably 1-butene), the total amount of ethylene and/or alpha-olefinbeing less than 10 mol %;

[0048] (c) polymers of conjugated diene monomers having from 4 to 12carbon atoms (preferably 1,3-butadiene, isoprene or mixtures thereof),possibly copolymerized with a monovinylarene having from 8 to 20 carbonatoms (preferably styrene) in an amount not higher than 50% by weight;

[0049] (d) homopolymers of monovinylarenes (in particular styrene) orcopolymers thereof with ethylene.

[0050] Functionalized monomers which may be used include for instance:silanes containing at least one ethylene unsaturation; epoxy compoundscontaining at least one ethylene unsaturation; monocarboxylic or,preferably, dicarboxylic acids containing at least one ethyleneunsaturation, or derivatives thereof, in particular anhydrides oresters.

[0051] Examples of silanes containing at least one ethylene unsaturationare: gamma-methacryloxypropyltrimethoxy-silane, allyltrimethoxy-silane,allyltriethoxy-silane, allylmethyldimethoxy-silane,allylmethyldiethoxy-silane, vinyltris(2-methoxyethoxy)-silane,vinyltrimethoxy-silane, vinylmethyldimethoxy-silane,vinyltriethoxy-silane, and the like, or mixtures thereof.

[0052] Examples of epoxy compounds containing at least one ethyleneunsaturation are: glycidyl acrylate, glycidyl methacrylate, itaconicacid monoglycidyl ester, maleic acid glycidylester, vinylglycidyl ether,allylglycidyl ether, and the like, or mixtures thereof.

[0053] Examples of monocarboxylic or dicarboxylic acids containing atleast one ethylene unsaturation are: maleic acid, maleic anhydride,fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylicacid, and the like, and anhydrides or esters derived therefrom, ormixtures thereof. Maleic anhydride is particularly preferred.

[0054] Polyolefins grafted with maleic anhydride are available ascommercial products identified for instance by the trademarks Fusabond®(Du Pont), Orevac® (Elf Atochem), Exxelor® (Exxon Chemical), Yparex®(DSM).

[0055] The elastomeric diene polymers usable as polymeric base in thepresent invention may be selected from those commonly used insulfur-vulcanizable elastomeric compositions, particularly suitable fortire manufacture, i.e. among unsaturated chain elastomeric polymers orcopolymers having a glass transition temperature generally lower than20° C., preferably comprised between 0° and −90° C. Such polymers orcopolymers may be of natural origin or may be obtained by solution oremulsion polymerization of one or more conjugated diolefins, possiblymixed with one or more monovinylarenes in an amount generally not higherthan 50% by weight.

[0056] Generally, the conjugated diolefins have from 4 to 12, preferablyfrom 4 to 8, carbon atoms, and may be selected from the groupcomprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like, or mixtures thereof. 1,3-butadieneand isoprene are particularly preferred.

[0057] Monovinylarenes possibly usable as comonomers generally have from8 to 20, preferably from 8 to 12 carbon atoms, and may be selected forinstance from: 1-vinylnaphthalene; 2-vinylnaphthalene; various alkyl,cycloalkyl, aryl, alkylaryl or arylalkyl styrene derivatives, such asfor instance: alpha-methylstyrene, 3-methylstyrene, 4-propylstyrene,4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene,4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, and the like, or mixturesthereof. Styrene is particularly preferred.

[0058] Preferably, the elastomeric diene polymers usable as a polymericbase in the present invention may be selected from: cis-1,4-polyisoprene(either natural or synthetic, preferably natural rubber),3,4-polyisoprene, poly-1,3-butadiene (in particular, high vinyl1,3-polybutadiene having a content of 1,2-polymerized units comprisedbetween 15 and 85% by weight), polychloroprene, possibly halogenatedisoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers,styrene/1,3-butadiene copolymers, 1,3-butadiene/isoprene copolymers,styrene/isoprene/1,3-butadiene copolymers, butadiene/acrylonitrilecopolymers, and the like, or mixtures thereof.

[0059] Diene polymers functionalized by reaction with suitableterminating or coupling agents may also be employed. In particular,diene polymers obtained by anionic polymerization in the presence of anorganometal initiator (in particular, an organo-lithium initiator) maybe functionalized by reaction of the organometallic residues derivingfrom the initiator with suitable terminating or coupling agents such asimines, carbodiimides, alkyltin halides, substituted benzophenones,alkoxy- or aryloxy silanes (see, for instance, European patentEP-451,604 and U.S. Pat. Nos. 4,742,124 and 4,550,142).

[0060] At least one reinforcing filler may be advantageously added tothe compositions according to the present invention, in an amountpreferably comprised between 0.1 and 120 phr, preferably between 20 and90 phr (phr=parts by weight per 100 parts of polymer base). Thereinforcing filler may be selected from those commonly employed forcross-linked products, and in particular for tires, such as: carbonblack, silica, alumina, aluminum silicates, calcium carbonate, kaolinand the like, or mixtures thereof. Carbon black, silica, or mixturesthereof are particularly preferred.

[0061] The carbon black grades usable according to the present inventionmay be selected from those conventionally used in tire manufacture,generally having a surface area not smaller than 20 m²/g (determined byCTAB absorption as described in ISO standard 6810).

[0062] The silica usable according to the present invention maygenerally be pyrogenic silica or, preferably, precipitated silica havinga BET surface area comprised between 50 and 500 m²/g, preferably between70 and 200 m²/g (measured according to ISO standard 5794/1).

[0063] If a reinforced filler comprising silica is present, thecomposition may advantageously incorporate a coupling agent capable ofinteracting with silica and to bind the latter to the polymer baseduring vulcanization.

[0064] Coupling agents of preferred use are those based on silane,identifiable for instance by the following structural formula:

(R)₃Si—C_(n)H_(2n)—X  (II)

[0065] wherein:

[0066] groups R, equal or different from each other, are selected from:alkyl, alkoxy, aryloxy groups or halogen atoms, with the proviso that atleast one of the R groups is an alkoxy or aryloxy group;

[0067] n is an integer of from 1 to 6;

[0068] X is a group selected from: nitrous, mercapto, amino, epoxy,vinyl, imido, chloro, —(S)_(m)—C_(n)H_(2n)—Si(R)₃, wherein m and n areintegers of from 1 to 6, and the R groups are as defined above.

[0069] Among them, the silane-based coupling agentbis(3-trietoxysilylpropyl)tetrasulfide (Si69) is particularly preferred,either as such or suitably mixed with a small amount of inert filler(for instance, carbon black) to facilitate the incorporation of the samein the rubber composition.

[0070] The compositions according to the present invention may bevulcanized according to known techniques, and in particular withsulfur-based vulcanizing systems commonly employed for diene elastomers.To this end, after a first thermal-mechanical working steps, asulfur-based vulcanizing agent is incorporated in the compositiontogether with vulcanization activators and accelerators. In this secondworking step, the temperature is generally kept below 120° C.,preferably below 100° C., to prevent undesired pre-cross-linkingphenomena.

[0071] The vulcanizing agent of most advantageous use is sulfur orsulfur-containing molecules (sulfur donors) with accelerators andactivators known to anyone skilled in the art.

[0072] Particularly effective activating agents are zinc compounds andin particular ZnO, ZnCO₃, zinc salts of fatty acids, saturated orunsaturated, having from 8 to 18 carbon atoms, such as for instance zincstearate, preferably formed in situ in the rubber composition startingfrom ZnO and fatty acid, as well as BiO, PbO, Pb₃O₄, PbO₂, and mixturesthereof.

[0073] Accelerators of common use may be selected from:dithiocarbamates, guanidines, thioureas, thiazoles, sulphenamides,tiourams, amines, xanthates, and the like, or mixtures thereof.

[0074] The compositions according to the present invention may includeother additives of common use selected on the basis of each specificapplication they are intended for. For instance, the following may beadded to said compositions: antioxidants, antiageing agents,plasticizers, adhesive agents, antiozonants, modifying resins, fibers(for instance, Kevlar® pulp), and the like.

[0075] In particular, in order to further improve processability, alubricant, generally selected from mineral oils, vegetable oils,synthetic oils and the like, or mixtures thereof, for instance: aromaticoil, naphthene oil, phthalates, soybean oil, and the like, may be addedto the cross-linking compositions of the present invention. The amountof the lubricant may generally range between 2 and 100 phr, preferablybetween 5 and 50 phr.

[0076] The preparation of the compositions according to the presentinvention may be carried out by mixing the polymer components with thepossibly present reinforcing filler and the other additives according totechniques known in the art. Mixing may be carried out for instance bymeans of an open-mill type mixer, or by means of an internal mixer ofthe type with tangential (Banbury) or interpenetrating (Intermix)rotors, or in continuous mixers of the Ko-Kneader (Buss) type, or oftwin-screw co-rotating or counter-rotating type.

[0077] The hydrophilic polymer and the functionalized polymer may beused in the form of powder, beads or pellets. In order to improve mixingwith the other components, such polymers may be used combined with aplasticizer, such as glycerin, pentaerythrite, and the like. Preferably,the compositions according to the present invention are produced in twosteps. In a first step, the mixture of the hydrophilic polymer and ofthe functionalized polymer is prepared, possibly with a portion of theelastomeric base, thereby forming a masterbatch. In a subsequent step,the masterbatch is mixed with the remaining portion of the elastomericbase and the other components, according to conventional methods. Thefirst step of masterbatch preparation is preferably carried out in acontinuous mixer, for instance a twin-screw extruder, at a temperatureof more than 120° C., so as to obtain an excellent dispersion of thethermoplastic polymers in the elastomeric base. The continuous mixers ofpreferred use are characterized by an adjustable geometry of the screwand thermal profile of the cylinder.

[0078] Now, the present invention will be further illustrated by someexamples, with reference to:

[0079] the attached FIG. 1, which shows a partly interrupted view incross-section of a tire according to the invention.

[0080] With reference to FIG. 1, a tire 1 conventionally comprises atleast one carcass ply 2 whose opposite side edges are externally bentaround respective bead wires 3, each incorporated in a bead 4 along acircumferential internal edge of the tire, at which said tire engages ona rim 5 which makes part of a vehicle wheel.

[0081] Along the circumferential development of the carcass ply 2 one ormore belt strips 6, made of textile or metal chords incorporated in asheet of rubber composition, are applied. Externally to the carcass ply2, in respective opposite side portions of the same, a couple ofsidewalls 7 is applied, each of which extends from the bead 4 up to aso-called “shoulder” zone 8 of the tire, defined at the opposite ends ofthe belt strip 6. A tread 9, whose side edges terminate at the shoulders8, connecting with the side walls 7, is circumferentially applied on thebelt strips 6. The tread 9 is externally provided with a rolling surface9 a, intended for getting in touch with the ground, whereincircumferential grooves 10 may be formed, intercalated with transversalslits, not shown in the attached FIGURE, which define a plurality ofblocks 11, variously distributed on said rolling surface 9 a.

[0082] The production process of the tire according to the presentinvention may be carried out with techniques and apparatuses known inthe art. More particularly, such process comprises an assembling step ofthe green tire, wherein several semi-finished products, previously andseparately prepared from each other and corresponding to the differentparts of the tire (carcass plies, belt strips, bead wires, fillings,sidewalls and treads) are associated with each other with a suitableassembling machine.

[0083] Afterwards, the green tire thus obtained is transferred to thesubsequent shaping and cross-linking steps. To this end, a vulcanizationmold is used, adapted to house the tire under working within a moldingcavity having walls counter-shaped with respect to the outer surface ofthe tire once the cross-linking has been completed.

[0084] Shaping of the green tire may be carried out by feeding apressurized fluid into the space defined by the tire inner surface, inorder to press the outer surface of the green tire against the walls ofthe molding cavity. In one of the most widely used shaping methods, avulcanization chamber made of elastomeric material, filled with vaporand/or other fluids, is inflated within the tire enclosed in the moldingcavity. In this way, the green tire is pushed against the inner walls ofthe molding cavity, obtaining the desired shaping. Alternatively,shaping may be carried out without an inflatable vulcanization chamber,by preparing within the tire a toroidal metal support shaped inaccordance to the configuration of the inner surface of the tire to beobtained (see for instance patent EP-242 840). The different coefficientof thermal expansion between the toroidal metal support and the greenelastomeric material is exploited to achieve an adequate moldingpressure.

[0085] At this point, the cross-linking step of the green elastomericmaterial present in the tire is carried out. To this aim, the outer wallof the vulcanization mold is caused to get in touch with a heating fluid(generally, vapor), so that the outer wall reaches a maximum temperaturegenerally comprised between 100° C. and 230° C. At the same time, theinner surface of the tire is brought to the cross-linking temperaturewith the same pressurized fluid employed to press the tire against thewalls of the molding cavity, heated up to a maximum temperaturecomprised between 100 and 250° C. The time necessary to obtain asatisfactory degree of cross-linking throughout the mass of theelastomeric material may generally range between 3 min and 90 min, andmainly depends on the tire size.

[0086] Some embodiments of the present invention are reported in thefollowing.

EXAMPLES 1-3 Preparation of a Masterbatch Comprising the HydrophilicPolymer

[0087] Compositions according to the present invention (masterbatch)were prepared as shown in Table 1. For comparison, compositions werealso prepared which contained the hydrophilic polymer but not thefunctionalized polymer (Example 2) and compositions which contained thehydrophilic polymer combined with a polymer that had no reactivefunctional groups (Example 3).

[0088] A mixture of the ingredients reported in Table 1 (the amounts areexpressed as % by weight of the total) was fed to a parallel twin-screw(co-rotating) extruder having a length/diameter ratio L/D=30. Themaximum temperature reached during the extrusion was of 200° C.±5° C.The masterbatch was air cooled.

[0089] The compositions thus obtained were analyzed with an opticalmicroscope in order to evaluate the dispersion of the hydrophilicpolymer within the elastomeric matrix, according to the followingmethod.

[0090] Preparation of Samples

[0091] A 3 g sample of each composition was pressure-molded in aPrestopress-Struers press (conditioning time: 15 min; pressure=1 atm;maximum temperature=110° C.).

[0092] From the discs thus obtained, sections having a thickness of 5 μmwere obtained using a Reichert-Jung 2050 microtome equipped with a LN20cryogenic unit (cutting temperature: −70° C.). The sections thusobtained were placed on a slide previously cooled at −70° C.

[0093] Optical Analysis

[0094] The sections thus prepared were observed with a transmissionoptical microscope with polarized light (Polyvar Met model; 10× lenses,multiplication factor=1, equipped with polarizer and analyzer). Twentyimages for each sample were memorized through a JVC TK1280E videocamerawith a Y/C connecting cable. The images were computer-analyzed (by meansof an Image Pro Plus—Media Cybernetic software), measuring for theparticles having a clear color, corresponding to domains containing thehydrophilic polymer, the mean area and mean diameter values, and themean number of particles per surface unit of the sample. The results arereported in Table 1. TABLE 1 Example 1 2 (*) 3 (*) SBR 75 75 75 PVA 1925 19 PE-MA 6 — — PEB — — 6 Microscope analysis Average area (μm²)145.94 328.12 220.10 No. of particles (mm⁻²) 1788.90 689.50 1121.23Average diameter (μm) 11.98 14.12 12.71

EXAMPLES 4-6 (Silica-Containing Rubber Compositions)

[0095] Sulfur-vulcanizable silica-containing rubber compositions wereprepared. The compositions are reported in Table 2A (in phr). Withrespect to the reference rubber composition containing 70 phr of silica(Example 4), the rubber compositions of Examples 5-6 contain 6.3 phr ofPVA according to the invention (Example 5) or 6.3 phr of starch/PVAcomposite according to U.S. Pat. No. 5,672,639 (Example 6) instead of 10phr of silica. The amounts expressed in phr of silica and of hydrophilicpolymers are not equal, since, as known, to evaluate the reinforcingproperties of a filler, reference must be made to the parts by volumeand not to the parts by weight.

[0096] All the ingredients, except for sulfur and the accelerators weremixed in an internal mixer (model Pomini PL 1.6) for about 5 min (1^(st)step). As soon as the temperature of 145±5° C. was reached, the rubbercomposition was discharged. Thereafter, sulfur and the acceleratingagents were added by mixing in a laboratory cylinder open mixer (2^(nd)step). TABLE 2A Example 4 (*) 5 6 (*) 1^(st) step SBR 84 65.3 84 BR 3939 39 SiO₂ 70 60 60 Masterbatch (Ex. 1) — 25 — Starch/PVA — — 6.3 Silane5.6 5.6 5.6 Stearic acid 2 2 2 ZnO 2.5 2.5 2.5 Aromatic oil 5 5 5Antioxidant 2 2 2 Microcrystalline wax 1 1 1 2^(nd) step Sulfur 1.4 1.41.4 DPG 1.9 1.9 1.9 CBS 1.8 1.8 1.8

[0097] The compositions thus prepared were submitted to MDR rheometricanalysis utilizing a Monsanto MDR rheometer, carrying out the tests at151° C. for 60 min with an oscillation frequency of 1.66 Hz (100oscillations per minute) and an oscillation amplitude of ±0.50°. Themechanical properties (according to ISO standard 37) and the hardness inIRHD degrees at 23° C. and 100° C. (according to ISO standard 48) weremeasured on samples of the aforesaid compositions cross-linked at 151°C. for 30 minutes. The results are shown in Table 2B.

[0098] Table 2B also shows the dynamic elastic properties, measured witha dynamic Instron device in the traction-compression mode according tothe following method. A test piece of the cross-linked material having acylindrical form (length=25 mm; diameter=14 mm), compression-preloadedup to a 10% longitudinal deformation with respect to the initial length,and kept at the prefixed temperature (70° C. or 10° C.) for the wholeduration of the test, was submitted to a dynamic sinusoidal strainhaving an amplitude of ±3.33% with respect to the length under pre-load,with a 100 Hz frequency. The dynamic elastic properties are expressed interms of dynamic elastic modulus (E′) and tandelta (loss factor) values.As is known, the tandelta value is calculated as a ratio between theviscous modulus (E″) and the elastic modulus (E′), both of them beingdetermined with the above dynamic measurements.

[0099] Lastly the DIN abrasion values were measured according to ISOstandard 4649, also reported in Table 2B, expressed as relativevolumetric loss with respect to the reference composition of Example 4(assumed to be 100). TABLE 2B Example 4 (*) 5 6 (*) Rheometricproperties Max torque (dN · m) 23.1 22.2 21.8 Min. torque (dN · m) 3.02.3 2.7 Delta torque (dN · m) 20.1 19.9 19.1 t90 (min) 21.0 20.0 30.0Mechanical properties 100% Modulus (MPa) 2.50 2.70 3.07 300% Modulus(MPa) 9.59 9.55 10.05 Stress at break (MPa) 16.20 15.30 13.80 Elongationat break (%) 485 435 395 300% Mod./100% Mod. 3.8 3.5 3.3 Dynamicproperties E′ (70° C.) (MPa) 6.20 6.39 6.25 E′ (10° C.) (MPa) 8.42 9.468.51 Tandelta (70° C.) 0.112 0.095 0.093 Tandelta (10° C.) 0.270 0.2540.238 IRHD hardness at 23° C. 74 73 74 IRHD hardness at 100° C. 69 68 69DIN abrasion 100 105 125

EXAMPLES 7-9 (Rubber Compositions Containing Carbon Black)

[0100] Sulfur-vulcanizable rubber compositions containing carbon blackwere prepared with the same method described for Examples 4-6. Thecompositions thus obtained are reported in Table 3A (in phr). Withrespect to the reference rubber composition containing 70 phr of carbonblack (Ex. 7), the rubber compositions of Examples 8-9 contain 7 phr ofPVA according to the invention (Ex. 8) or 7 phr of starch/PVA compositeaccording to U.S. Pat. No. 5,672,639 (Ex. 9), instead of 10 phr ofcarbon black.

[0101] The same measurements of Examples 4-6 were carried out on therubber compositions thus obtained. The results are shown in Table 3B.TABLE 3A Example 7 (*) 8 9 (*) 1^(st) step SBR 84 63 84 BR 39 39 39 C.B.70 60 60 Masterbatch (Ex. 1) — 28 — Starch/PVA — — 7 Silane — 0.7 0.7Stearic acid 2 2 2 ZnO 2.5 2.5 2.5 Aromatic oil 5 5 5 Antioxidant 2 2 2Microcristalline wax 1 1 1 2^(nd) step Sulfur 1.4 1.4 1.4 DPG 1.9 1.91.9 CBS 1.8 1.8 1.8

[0102] TABLE 3B Example 7 (*) 8 9 (*) Rheometric properties Max torque(dN · m) 21.2 18.7 17.8 Min. torque (dN · m) 4.4 3.4 3.6 Delta torque(dN · m) 16.6 15.3 14.2 t90 (min) 13.3 11.9 11.8 Mechanical properties100% Modulus (MPa) 3.17 3.10 2.85 300% Modulus (MPa) 13.30 12.10 11.00Stress at break (MPa) 15.80 15.10 13.32 Elongation at break (%) 380 403375 300% Mod./100% Mod. 4.2 3.9 3.9 Dynamic properties E′ (70° C.) (MPa)7.51 6.78 6.31 E′ (10° C.) (MPa) 12.83 11.72 11.10 Tandelta (70° C.)0.191 0.173 0.170 Tandelta (10° C.) 0.337 0.316 0.320 IRHD hardness at23° C. 75 74 72 IRHD hardness at 100° C. 70 67 66 DIN abrasion 100 115130

EXAMPLES 10-11 (Rubber Compositions Containing Silica and Carbon Black)

[0103] Sulfur-vulcanizable rubber compositions containing silica andcarbon black were prepared with the same method described for Examples4-6. The compositions are reported in Table 4A (in phr).

[0104] The same measurements of Examples 4-6 were carried out on therubber compositions thus obtained.

[0105] Additionally, the water absorption capacity of the preparedrubber compositions was also evaluated with the following method.

[0106] A sample of rubber composition was vulcanized in a press heatedto 151° C. for 30 min. Polytetrafluoroethylene sheets were interposedbetween the rubber composition and the press platens to prevent anycontamination and adhesion of said rubber composition. Sheets measuring120×120 mm and having a thickness of about 1.0 mm were obtained in thisway. Rectangular samples measuring 60×30 mm were cut from these sheets.Said samples were oven-dried at 65° C. for 48 hours and then exposed todry air in a dry-box at room temperature for 48 hours. The weight of thesamples so dried was registered. The samples were then immersed in waterat two different temperatures (4° C. and 23° C.) and their weight wasmeasured after 28, 51 and 118 hours of immersion. Table 4C shows theresults obtained, expressed as percent variation of the weight based onthe starting weight. TABLE 4A Example 10 (*) 11 1^(st) step SBR 75 53 BR25 25 SiO₂ 35 35 C.B. 35 25 Masterbatch (Ex. 1) — 29 Silane 3.5 3.5Stearic acid 2 2 ZnO 3 3 Aromatic oil 15 15 Antioxidant 2 2Microcristalline wax 1 1 2^(nd) step Sulfur 1.2 1.2 CBS 2.5 2.5

[0107] TABLE 4B Example 10 (*) 11 Max torque (dN · m) 16.5 16.4 Min.torque (dN · m) 3.1 2.6 Delta torque (dN · m) 13.4 13.8 t90 (min) 15.015.0 100% Modulus (MPa) 2.5 2.6 300% Modulus (MPa) 11.0 11.2 Stress atbreak (MPa) 17.3 16.4 Elongation at break (%) 474 456 300% Mod./100%Mod. 4.4 4.3 E′ (70° C.) (MPa) 6.1 6.0 E′ (10° C.) (MPa) 14.9 15.5Tandelta (70° C.) 0.230 0.200 Tandelta (10° C.) 0.609 0.569 IRHDhardness at 23° C. 75 74 IRHD hardness at 100° C. 63 62 DIN abrasion 100102

[0108] TABLE 4C Example 10 (*) 11 Immersion in water at 23° C.  28 hours1.1 1.7  51 hours 1.7 2.3 118 hours 2.3 3.2 Immersion in water at 4° C. 28 hours 0.8 1.0  51 hours 1.1 1.3 118 hours 1.4 1.8

[0109] From the experimental results reported above, the following maybe noticed.

[0110] The presence of the functionalized polymer ensures an excellentdispersion of the hydrophilic polymer throughout the polymer matrix, asproved by optical analysis (Ex. 1-3, Tab. 1).

[0111] In the rubber compositions containing silica as a reinforcingfiller, the partial replacement of silica with a combination ofhydrophilic polymer and functionalized polymer according to the presentinvention allows to achieve, with respect to similar compositionswherein a destructured starch/PVA composite is employed, a more markedreinforcing effect, as evidenced by the high modulus values, inparticular at high elongation, 300% modulus/100% modulus ratio andstress at break. The cross-linked product also shows improved hystereticproperties, in particular higher tandelta values at 100C with the samevalues of tandelta at 70° C. (i.e. a better road grip on wet groundswith the same rolling resistance). These effects have been achievedwithout significantly worsening abrasion resistance.

[0112] The reinforcing effect of the hydrophilic polymer according tothe present invention remains in any event high also when thehydrophilic polymer partly replaces carbon black, which, as known, is aparticularly effective reinforcing filler. This is proved by themechanical properties (modulus, elongation and stress at break) and bythe abrasion resistance, which maintains with values comparable to thoseof the compositions only containing carbon black. The same effect isobtained by employing the destructured starch/PVA composite (seeExamples 7-9, Tables 3A-3B).

[0113] The same behavior is achieved with rubber compositions reinforcedwith mixtures of silica and carbon black (see Examples 10-11, Tables4A-4B).

[0114] Without being bound in any way to any interpretative theory, theApplicant believes that the improved reinforcing capabilities of thehydrophilic polymer combined with the functionalized polymer accordingto the present invention with respect to the plasticized destructuredstarch are due to an improved interaction of the hydrophilic polymerwith the elastomeric matrix and with the reinforcing filler, if present.Conversely, destructured starch tends to favor intramolecularinteraction to the detriment of interactions with the elastomeric matrixand with the reinforcing filler, so that it turns out to be poorlycompatibilized within the cross-linked material.

1. A tire for vehicle wheels comprising at least one element made of anelastomeric material, characterized in that said element includes acomposition comprising: (a) at least one elastomeric diene polymer; (b)at least one thermoplastic polymer having a main hydrocarbon chain towhich hydrophilic groups are linked; (c) at least one polymer containingfunctional groups reactive with said hydrophilic groups.
 2. The tireaccording to claim 1, wherein said element including said composition isa tread belt.
 3. The tire according to anyone of the preceding claims,wherein the hydrophilic polymer is present in the composition in anamount comprised between 0.1 and 100 phr.
 4. The tire according toanyone of the preceding claims, wherein the functionalized polymer ispresent in the composition in an amount so as to obtain a weight ratiobetween the hydrophilic polymer and the functionalized polymer comprisedbetween 0.5:1 and 10:1.
 5. The tire according to anyone of the precedingclaims, wherein the hydrophilic polymer comprises hydrophilic groupsselected from: hydroxyl groups —OH; carboxylic groups —COOH, possibly atleast partially in the salt form; ester groups —COOR (R=alkyl orhydroxyalkyl); amide groups —CONH₂; sulfonic groups —SO₃H, possibly atleast partially in the salt form.
 6. The tire according to anyone of thepreceding claims, wherein the hydrophilic polymer is capable ofabsorbing at least 0.1% by weight of water based on the polymer weightafter a 24-hour exposure in an environment having a 50% relativehumidity at the temperature of 24° C. (according to ASTM standard D570).7. The tire according to anyone of the preceding claims, wherein thehydrophilic polymer has a melting temperature lower than 230° C.
 8. Thetire according to anyone of the preceding claims, wherein thehydrophilic polymer is selected from: polyacrylic acid, polymethacrylicacid, polyhydroxy-alkylacrylate, polyalkylacrylate, polyacrylamide,acrylamide/acrylic acid copolymers, polyvinylalcohol, polyvinylacetate,vinylalcohol/vinylacetate copolymers, ethylene/vinylacetate copolymers,ethylene/vinylalcohol copolymers, ethylene/vinylalcohol/vinylacetateterpolymers, polyvinylsulfonic acid, polystyrene sulfonate, and mixturesthereof.
 9. The tire according to anyone of the preceding claims,wherein the hydrophilic polymer comprises repeating units having theformula:

with a random or block distribution along the chain.
 10. The tireaccording to claim 9, wherein the hydrophilic polymer is selected from:(i) vinylalcohol polymers obtained by hydrolysis of polyvinylacetate,with a hydrolysis degree comprised between 50 and 100 mol %; (ii)ethylene/vinylalcohol copolymers having a content of ethylene unitscomprised between 20 and 60 mol %.
 11. The tire according to anyone ofthe preceding claims, wherein the functionalized polymer is athermoplastic hydrocarbon polymer having functional groups selectedfrom: carboxylic groups, anhydride groups, ester groups, silane groups,epoxy groups.
 12. The tire according to anyone of the preceding claims,wherein the functionalized polymer has an amount of functional groupscomprised between 0.05 and 50 parts by weight, based on 100 parts byweight of the polymer.
 13. The tire according to anyone of the precedingclaims, wherein the composition comprising the hydrophilic polymerfurther includes at least one reinforcing filler.
 14. The tire accordingto claim 13, wherein the reinforcing filler is carbon black.
 15. Thetire according to claim 13, wherein the reinforcing filler is silica.16. The tire according to claim 13, wherein the reinforcing filler is amixture of carbon black and silica.
 17. The tire according to claim 15or 16, wherein the composition comprising the hydrophilic polymerfurther includes a silica coupling agent.
 18. The tire according toanyone of the preceding claims, wherein the composition comprising thehydrophilic polymer is cross-linked by means of a sulfur-basedvulcanizing agent.
 19. An elastomeric composition comprising: (a) atleast one elastomeric diene polymer; (b) at least one thermoplasticpolymer having a main hydrocarbon chain to which hydrophilic groups arelinked; (c) at least one polymer containing functional groups reactivewith said hydrophilic groups.
 20. The composition according to claim 19,wherein the hydrophilic polymer is present in an amount comprisedbetween 0.1 and 100 phr.
 21. The composition according to anyone ofclaims from 19 to 20, wherein the functionalized polymer is included inan amount so as to obtain a weight ratio between the hydrophilic polymerand the functionalized polymer comprised between 0.5:1 and 10:1.
 22. Thecomposition according to anyone of claims from 19 to 21, wherein thehydrophilic polymer comprises hydrophilic groups selected from: hydroxylgroups —OH; carboxylic groups —COOH, possibly at least partially in thesalt form; ester groups —COOR (R=alkyl or hydroxyalkyl); amide groups—CONH₂; sulfonic groups —SO₃H, possibly at least partially in the saltform.
 23. The composition according to anyone of claims from 19 to 22,wherein the hydrophilic polymer is capable of absorbing at least 0.1% ofwater based on the polymer weight, after a 24-hour exposure in anenvironment having a 50% relative humidity at the temperature of 24° C.(according to ASTM standard D570).
 24. The composition according toanyone of claims from 19 to 23, wherein the hydrophilic polymer has amelting temperature lower than 230° C.
 25. The composition according toanyone of claims from 19 to 24, wherein the hydrophilic polymer isselected from: polyacrylic acid, polymethacrylic acid,polyhydroxy-alkylacrylate, polyalkylacrylate, polyacrylamide,acrylamide/acrylic acid copolymers, polyvinylalcohol, polyvinylacetate,vinylalcohol/vinylacetate copolymers, ethylene/vinylacetate copolymers,ethylene/vinylalcohol copolymers, ethylene/vinylalcohol/vinylacetateterpolymers, polyvinylsulfonic acid, polystyrene sulfonate, and mixturesthereof.
 26. The composition according to anyone of claims from 19 to25, wherein the hydrophilic polymer comprises repeating units having theformula:

with a random or block distribution along the chain.
 27. The compositionaccording to claim 26, wherein the hydrophilic polymer is selected from:(i) vinylalcohol polymers obtained by hydrolysis of polyvinyl acetate,with a hydrolysis degree comprised between 50 and 100 mol %; (ii)ethylene/vinylalcohol copolymers having a content of ethylene unitscomprised between 20 and 60 mol %.
 28. The composition according toanyone of claims from 19 to 27, wherein the functionalized polymer is athermoplastic hydrocarbon polymer having functional groups selectedfrom: carboxylic groups, anhydride groups, ester groups, silane groups,epoxy groups.
 29. The composition according to anyone of claims from 19to 28, wherein the functionalized polymer has an amount of functionalgroups comprised between 0.05 and 50 parts by weight, based on 100 partsby weight of polymer.
 30. The composition according to anyone of claimsfrom 19 to 29, comprising at least one reinforcing filler.
 31. Thecomposition according to claim 30, wherein the reinforcing filler iscarbon black.
 32. The composition according to claim 30, wherein thereinforcing filler is silica.
 33. The composition according to claim 30,wherein the reinforcing filler is a mixture of carbon black and silica.34. The composition according to claim 32 or 33, further comprising asilica coupling agent.
 35. The composition according to anyone of claimsfrom 9 to 34, further comprising a sulfur-based vulcanizing agent.